1. Field of Invention
The present invention relates generally to portable computing devices. More particularly, the present invention relates to an apparatus for reducing electromagnetic interference (EMI) noise emitted from a portable computing device.
2. Description of the Related Art
Advances in technology have enabled the size of personal computers to decrease. As a result, the use of portable computers such as notebook, or laptop, computers and notepad computers is rapidly increasing. The portability of notebook computers and notepad computers enables a user to keep his or her computer readily accessible such that computing resources are effectively always at hand. By way of example, a notebook computer running on a battery pack enables a user to access computational resources without the need for external sources of electricity.
Many portable computers are configured such that a display screen of the computer pivots, or rotates, with respect to the base of the computer. FIG. 1 is a diagrammatic representation of a portable computer or, more specifically, a notebook computer. A notebook computer 102 generally includes a display section 106 and a base section 110. Display section 106 typically includes a display screen 114, while base section 110 often includes an input/output device such as a keyboard 118, and houses a central processing unit and memory devices (not shown).
In general, within notebook computer 102, circuitry associated with base section 110 must be electrically coupled to circuitry associated with display section 106. As such, within notebook computer 102, a cable mechanism (not shown) is often used to facilitate the transfer of signals, e.g., signals associated with low voltage differential signaling (LVDS), between base section 110 and display section 106.
In order to maintain a relatively small size for notebook computer 102, relatively thin, or low-profile, cable mechanisms are typically used to facilitate the transfer of LVDS signals within notebook computer 102. For many portable computing devices, a flexible circuit such as a polyemide flexible circuit may be used due to its flexible characteristics and low profile. However, a polyemide flexible circuit does not have any inherent electromagetic compatibility (EMC) shielding within it. As a result, electromagnetic interference (EMI) emissions, such as emissions which may be in the range of approximately 100 megaHertz (MHz) to approximately 1000 MHz, generally result from the LVDS signals associated with a polyemide flexible circuit with no shielding.
EMI is typically characterized as electromagnetic emissions from a device, e.g., notebook computer 102, which have the tendency to interfere with the operation of another device or system. By way of example, EMI emissions from notebook computer 102 may interfere at relatively close range with FM radio reception, television reception, controls on an aircraft such as a rudder control, and operations of a cellular telephone. EMI emissions may result from an LVDS signal, as a cable mechanism which carries an LVDS signal acts as a noisy antenna which picks up EMI noise in base section 110 and pipes the EMI noise out of notebook computer 102.
As will be understood by those skilled in the art, a section of notebook computer 102 that is particularly susceptible to emitting EMI is a xe2x80x9cjunctionxe2x80x9d 130 between base section 110 and display section 106 which effectively separates base section 110 and display section 106. A small gap (not shown) is often a part of junction 130, and acts as an xe2x80x9cemissions pointxe2x80x9d that is characterized by a relatively large amount of irradiated EMI emissions. Typically, the emissions point is located at approximately the area through which a cable mechanism that transfers signals between base section 110 and display section 106 passes.
A cable mechanism which serves as a conduit between base section 110 and display section 106 generally has a higher level of EMI emissions than other cable mechanisms that may be associated with notebook computer 102. This higher level of EMI emissions is due, at least in part, to the fact that the cable mechanism between base section 110 and display section 106 has a substantially vertical orientation while LVDS signals are being transferred between base section 110 and display section 106. In other words, the fact that at least part of the cable mechanism or flexible circuit, i.e., the part in display section 106, is oriented along a y-axis 134 during the operation of notebook computer 102 typically provides increased EMI emissions relative to other cables within notebook computer 102.
In order to lower the amount of EMI emissions associated with cable mechanisms such as a flexible circuit, ferrite may be added in proximity to the emissions point or junction 130 associated with notebook computer 102. The ferrite effectively absorbs energy, and blocks at least some EMI emissions. Hence, the use of a ferrite block or wrapping may provide at least some EMC shielding. While the use of ferrite has been observed as being relatively effective, ferrite blocks often have a high profile, i.e., ferrite blocks often have at least one physical dimension such as a thickness which is large with respect to the dimensions of notebook computer 102. In other words, ferrite blocks generally occupy more space than is acceptable within notebook computer 102. Additionally, ferrite blocks are relatively expensive, and may cause undesirable pooling, or visible swirls, in the liquid crystal displays which are often associated with display section 106.
Therefore, what is needed is a low profile, relatively inexpensive cable mechanism for transferring LVDS signals without producing significant EMI emissions within a portable computing device.
The present invention relates to a cable which enables electromagnetic interference emissions to be reduced. According to one aspect of the present invention, a cable includes a first coaxial cable component, a second coaxial cable component, and a grounding plate. The first coaxial cable component has a first end and a second end, and includes a first shield. The second coaxial cable component also has a first end and a second end, and includes a second shield. The grounding plate is arranged to be conductively coupled, e.g., electrically coupled, to the first shield and the second shield, and is offset from the first end of the first coaxial cable component, the second end of the first coaxial cable component, the first end of the second coaxial cable component, and the second end of the second coaxial cable component. In one embodiment, the grounding plate is also arranged to contact a ground source.
In another embodiment, the cable includes a first connector that is coupled to the first end of the first coaxial cable component. The first connector is also coupled to the first end of the second coaxial cable component. In such an embodiment, the first connector may include a grounding shield that is arranged to be conductively coupled to the first shield at the first end of the first coaxial cable component and to the second shield at the first end of the second coaxial cable component.
A cable which enables contact to be made between a grounding plate and a ground source provides for the transmission of low voltage differential signals while being relatively immune to noise, reducing the emission of electromagnetic interference. Reducing the emission of electromagnetic interference enables a device, e.g., a portable computing device, which uses the cable to operate without significantly affective the performance of other devices in proximity to the cable.
According to another aspect of the present invention, a computing system includes a base portion, a display portion, and a cable assembly. The base portion includes a central processing unit and a first receptacle, while the display portion includes a display screen, a second receptacle, and a first conductive surface. The cable assembly has a first end and a second end, and includes a plurality of coaxial cables as well as a first grounding plate. Each coaxial cable included in the plurality of coaxial cables includes a shield that is conductively coupled to the first grounding plate, which is essentially in direct contact, e.g., in electrical contact, with the first conductive surface. The first end is arranged to interface with the first receptacle and the second end being arranged to interface with the second receptacle such that the cable assembly is effectively xe2x80x9cplugged intoxe2x80x9d the first receptacle and the second receptacle.
In one embodiment, the cable assembly is arranged to enable a data signal to pass between the base portion and the display portion, and the substantially direct contact between the first grounding plate and the first conductive surface is arranged to reduce the emission of electromagnetic interference associated with enabling the data signal to pass between the base portion and the display portion. In such an embodiment, the data signal may be a low voltage differential signal.
According to still another aspect of the present invention, an overall cable includes first and second microcoaxial cable components, as well as first and second connectors. The first and second microcoaxial cable components each include a shield and a center conductor, and each have a first end and a second end. The first connector is coupled to the shield and the center conductor of the first cable component at the first end of the first cable component. The first connector is also being coupled to the shield and the center conductor of the second cable at the first end of the second cable. The second connector is coupled to the shield and the first center conductor at the second end of the first cable, and is also coupled to the shield and the second center conductor at the second end of the second cable.
In one embodiment, the overall cable includes a grounding plate that is conductively coupled to the shield of the first cable and the shield of the second cable. The grounding plate is generally positioned such that it is not in direct physical contact with the first connector or the second connector. In such an embodiment, the grounding plate may be coupled only to a portion of the first shield and a portion of the second shield.